I found that Tektro cartridge style pads have the noodle on the back to locate it into the eccentric adjuster.
I think any current Shimano style shoe (including Tektro and Ashima copies) should fit, but probably need a different bolt as the normal bolt head looks too big to fit the recess in the eccentric adjuster. Of course, they won't look as cool as the stock ones, but you get to use common pattern pads, including modern compounds which might actually slow you down with a single pivot calliper, and you can buy generic Shimano copies for under £8 http://www.ribblecycles.co.uk/sp/road-track-bike/Brake-Pads-Rim-Trivio-453-Caliper-Brake-Blocks-Cart-System-1pr/TRIVBRBL200
I think any current Shimano style shoe (including Tektro and Ashima copies) should fit, but probably need a different bolt as the normal bolt head looks too big to fit the recess in the eccentric adjuster. Of course, they won't look as cool as the stock ones, but you get to use common pattern pads, including modern compounds which might actually slow you down with a single pivot calliper, and you can buy generic Shimano copies for under £8
http://www.ribblecycles.co.uk/sp/road-track-bike/Brake-Pads-Rim-Trivio-453-Caliper-Brake-Blocks-Cart-System-1pr/TRIVBRBL200